<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>for</title>
</head>
<body>
    <script>
        var sum = 0;
        for (var i = 1; i <= 100; i++){
            sum +=i ;
        }
        alert(sum)
    </script>
</body>
</html>